PROJECT SUMMARY Despite the availability of antibiotics to combat Tuberculosis (TB), it is one of the leading causes of death due to infectious disease. Mycobacterium tuberculosis (Mtb) is a successful pathogen because it survives within immune cells and effectively establishes and maintains a latent TB infection. Therefore, understanding the mechanisms underlying the establishment or maintenance of dormancy can inform new strategies for TB therapeutics. Mycobacterial membrane protein large (MmpL) proteins are dedicated cell wall lipid transporters. Along with their accessory Mycobacterial membrane protein small (MmpS) proteins, these transporters are crucial players in mycobacterial physiology and pathogenesis. MmpL3 is essential; and MmpL4, MmpL5, MmpL7, MmpL8, MmpL10 and MmpL11 contribute to Mtb virulence. The related proteins MmpL3 and MmpL11 that transport mycolic acid-containing lipids are of particular interest to us. MmpL3 transports trehalose monomycolate and is required for mycobacterial replication and viability. We showed that MmpL11 transports monomeromycolyl diacylglycerol and a mycolate ester wax. These are species of lipids that are sometimes referred to as ?storage lipids? and are associated with dormant bacteria in vitro and accumulate in granulomas of TB patients. Therefore, it appears that MmpL11 plays a role in a clinically relevant, but poorly understood, aspect of Mtb pathogenesis. While significant advances have been made identifying MmpL substrates, the regulation of MmpL protein expression and their role in cell wall remodeling in different environmental conditions has not been explored. The proposed studies will characterize the structure and function of Mtb transcriptional regulators that control expression of essential and virulence-associated MmpL and MmpS proteins. Our preliminary data indicate that fatty acids directly modulate activity of these unique transcription factors. This suggests a model where Mtb can directly assess and respond to fatty acid intermediates, metabolic state and nutrient availability to control mmpL and mmpS gene regulation. By defining the molecular mechanisms underlying the regulation of MmpL transporters and identifying their regulons, we will generate novel insights into the transition between actively dividing Mtb and latent or non-replicating persistent Mtb. !